Semiconductor memory device having open bit line structure

ABSTRACT

A semiconductor memory device has an array structure of an open bit line structure and comprises a plurality of normal memory mats, two dummy mats and a plurality of rows of sense amplifiers. The normal memory mat includes a plurality of memory cells and arranged in a bit line extending direction, while the dummy mat includes a plurality of dummy cells and arranged in a bit line extending direction at both ends of the plurality of normal memory mats. The rows of sense amplifiers are arranged between the normal memory mats and between each of the normal memory mats and each of the dummy mats. A first predetermined number of the dummy cells, the number of which is smaller than a number of the memory cells arranged along each bit line of the normal memory mats, are arranged along each bit line of the dummy mats.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor memory deviceconfigured to read and write data stored in memory cells, andparticularly relates to a semiconductor memory device employing an openbit line structure such as a DRAM (Dynamic Random Access Memory).

2. Description of Related Art

Conventionally, an open bit line structure and a folded bit linestructure have been known as an array structure employed in a memorycell array divided into a plurality of memory mats in a DRAM. In theDRAM of the open bit line structure, a pair of bit lines connected to asense amplifier is extended to memory mats different from each other.Meanwhile, in the DRAM of the folded bit line structure, a pair of bitlines connected to a sense amplifier is extended to the same memory mat.Generally, arrangement of memory cells of the folded bit line structureis restricted so that a cell size of each memory cell is supposed to belimited to 8F² (F is a minimum processing dimension). On the contrary,memory cells of the open bit line structure can be arranged at allintersections of word lines and bit lines so that each memory cell canbe formed with a cell size of 6F². Thus, it is appropriate to employ theopen bit line structure in order to improve integration of the DRAM. TheDRAM of the open bit line structure is configured with a structure inwhich a plurality of normal memory mats are aligned in a bit lineextending direction and end memory mats are arranged at both endsthereof. Each end memory mat has the same size as each normal memorymat, and due to its structure there are arranged dummy cells in a halfarea of the end memory mat. Thus, memory capacity of the end memory matis half that of the normal memory mat and the end memory mat has thesame size as the normal memory mat, thereby correspondingly decreasingarea efficiency of the DRAM. Meanwhile, a technique to improve the areaefficiency in the DRAM of the open bit line structure using a specialconfiguration of end memory mats has been proposed (for example, referto Patent Reference 1).

Patent Reference 1: Japanese Patent Application Laid-open No. 2007-5502

In the technique disclosed in the Patent Reference 1, the normal memorymats are formed with memory cells of 6F² having the open bit linestructure, and the end memory mats are formed with memory cells of 8F²having the folded bit line structure, thereby improving the areaefficiency without using dummy cells. However , when employing thetechnique disclosed in the Patent Reference 1, memory cells whose cellsize is 6F² and memory cells whose cell size is 8F² are mixed, and therearises a problem that process technique of the DRAM becomes complexbecause of a difference of memory cell structures. Further, inconsideration of the difference between memory cell structures of theend memory mat and the normal memory mat, the area of the end memorymats is merely about two-thirds of the area of the normal memory matseven if the dummy cells are not required, which is a problem ofdifficulty in remarkably improving the area efficiency.

SUMMARY

The present invention seeks to solve the above problems and provides asemiconductor memory device employing an open bit line structure, inwhich memory cell structure of end memory mats is common to that ofnormal memory mats and an area of the end memory mats is reduced so thatarea efficiency can be remarkably improved.

In one of aspects of the invention, there is provided a semiconductormemory device having an array structure of an open bit line structurecomprising: a plurality of normal memory mats each including a pluralityof memory cells, the normal memory mats aligned at least in a bit lineextending direction; two dummy mats each including a plurality of dummycells, the dummy mats arranged in a bit line extending direction at bothends of the plurality of normal memory mats; and a plurality of rows ofsense amplifiers arranged between the normal memory mats and betweeneach of the normal memory mats and each of the dummy mats. In thesemiconductor device, a first predetermined number of the dummy cells,the number of which is smaller than a number of the memory cellsarranged along each bit line of the normal memory mats, are arrangedalong each bit line of the dummy mats.

According to the aspects of the invention, in the memory cell arrayemploying the open bit line structure, dummy mats are arranged at bothends of normal memory mats and the plurality of dummy cells are arrangedin each dummy mat. Therefore, by arranging the first predeterminednumber of the dummy cells along each bit line forming a complimentarypair with a bit line of the normal memory mat, the first predeterminednumber can be remarkably smaller than the number of memory cellsarranged in the normal memory mat, thereby sufficiently reducing thesize of end memory mats.

As described above, according to the present invention, when employingthe open bit line structure in the semiconductor memory device, endmemory mats at both ends of the normal memory mats are used as dummymats so that a plurality of dummy cells are arranged therein. Therefore,the dummy mats can be decreased in size without requiring a large sizeof a conventional end memory mat so as to improve area efficiency.Further, since the structure of the dummy mat can be commonly used forthe normal memory mat, a simple array structure can be achieved withoutusing a complex process technology. Furthermore, each bit line of thedummy mat can have substantially the same resistance and capacitancevalues as those of each bit line of the normal memory mat, and thus areliable sensing operation can be maintained in an adjacent row of senseamplifiers.

BRIEF DESCRIPTION OF THE DRAWINGS

The above featured and advantages of the present invention will be moreapparent from the following description of certain preferred embodimentstaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a block diagram schematically showing a configuration of amemory cell array and its peripheral part in a DRAM of an embodiment;

FIG. 2 is a specific configuration of a part of the memory cell array ofFIG. 1;

FIG. 3 is a schematic circuit block diagram of the DRAM of theembodiment;

FIG. 4 is a partially enlarged block diagram showing the memory cellarray and its peripheral part in an arbitrary bank of the DRAM of theembodiment;

FIG. 5 is a first operation waveform diagram explaining control of adummy mat 11;

FIG. 6 is a second operation waveform diagram explaining the control ofthe dummy mat 11; and

FIG. 7 is a diagram showing an example of a partial layout of an areaincluding the dummy mat 11 in the memory cell array.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention will be now described herein with reference toillustrative embodiments. Those skilled in the art will recognize thatmany alternative embodiments can be accomplished using the teachings ofthe present invention and that the invention is not limited to theembodiments illustrated for explanatory purposes. In the following, anembodiment in which the present invention is applied to a DRAM as asemiconductor memory device will be described.

A configuration of a memory cell array in the DRAM of the embodimentwill be described with reference to FIGS. 1 and 2. FIG. 1 is a blockdiagram schematically showing the memory cell array and its peripheralpart, and FIG. 2 is a diagram showing a specific configuration of a partof the memory cell array of FIG. 1. The DRAM of the embodiment employsan open bit line structure as an array structure of the memory cellarray. An entire area of the memory cell array is divided into portions(for example, 16 portions) in a bit line extending direction (Xdirection shown in FIG. 1) and divided into portions (for example, 16portions) in a word line extending direction (Y direction shown in FIG.1). Then, dummy mats 11 serving as end memory mats are arranged at bothends of each group including a plurality of normal memory mats 10aligned in the X direction. For example, the entire area of the memorycell array is configured by arranging 16×16 normal memory mats 10 and2×16 dummy mats 11. In addition, the present invention can be applied toanother array structure in which the memory cell array is divided intoportions only in the X direction and is not divided into portions in theY direction.

FIG. 2 shows specific configurations of one normal memory mat 10 at theleft end and adjacent one dummy mat 11. In the normal memory mat 10, aplurality of (M) bit lines BL extending in the X direction and aplurality of (N) word lines WL extending in the Y direction arearranged, and a plurality of memory cells MC are formed at intersectionsthereof. For example, the normal memory mat 10 can be formed with256×512 memory cells MC by arranging 256 word lines WL and 512 bit linesBL. Each memory cell MC is composed of a transistor Q0 and a capacitorCs and has a cell size of 6F². The transistor Q0 has a gate connected toa word line WL, a source connected to a bit line BL, and a drainconnected to one terminal of the capacitor Cs. Further, the otherterminal of the capacitor Cs is connected to a predetermined potentialVs.

Meanwhile, in the dummy mat 11, M/2 bit lines /BL and M/2 dummy bitlines DBL respectively extending in the X direction are alternatelyarranged, and a predetermined number (the first predetermined number ofthe invention) of dummy cell control lines DCL are arranged. A pluralityof dummy cells DC are formed at intersections of the bit lines /BL, thedummy bit lines DBL and the dummy cell control lines DCL. In FIG. 2,four dummy cell control lines DCL(0) to DCL(3) are exemplified. In thiscase, the dummy mat 11 can be formed with, for example, 4×512 dummycells DC by alternately arranging 256 bit lines /BL and 256 dummy bitlines DBL and arranging four dummy cell control lines DCL(0) to DCL(3).

Each dummy cell DC, which is composed of a transistor Q0 and a capacitorCs, has the same size and structure as the above-mentioned memory cellMC and has the cell size of 6F². The transistor Q0 of the dummy cell DChas a gate connected to the dummy cell control line DCL, a sourceconnected to the bit line /BL or the dummy bit line DBL, and a drainconnected to one terminal of the capacitor Cs. The other terminal of thecapacitor Cs is connected to the predetermined potential Vs.

The number of dummy cells DC arranged along one bit line /BL or onedummy bit line DBL is in principal set within a range where a sum ofcapacitance values of the capacitors Cs (hereinafter refer to as “cellcapacitance Cs”) thereof can be controlled to be approximately the sameas that of a bit line capacitance Cb in the normal memory mat 10. Forexample, when the bit line capacitance Cb is 50 fF and the cellcapacitance Cs of each dummy cell DC is 25 fF, two dummy cells DC may bearranged along each bit line /BL or each dummy bit line DBL. However, itis possible to arrange a larger number of dummy cells DC on the premiseof controlling ON/OFF of the dummy cells DC in response to the dummycell control lines DCL as described later.

Returning to FIG. 1, a row of sense amplifiers 12 is arranged betweentwo adjacent normal memory mats 10. Similarly, the row of senseamplifiers 12 is also arranged between the normal memory mat 10 and thedummy mat 11. Each row of sense amplifiers 12 includes a plurality ofsense amplifiers SA aligned in the Y direction. The sense amplifier SAis connected to one bit line BL and one bit line /BL (hereinafter referto as “a pair of bit lines BL and /BL”) which form a complementary pair,and amplifies a voltage difference between both lines. In the row ofsense amplifiers 12, there are arranged N/2 sense amplifiers SA eachconnected to the pair of bit lines BL and /BL.

As shown in FIG. 2, in the normal memory mat 10 adjacent to the dummymat 11 at the left end, the bit lines BL are connected to the senseamplifiers SA of the row of sense amplifiers 12 on the left side, thebit lines /BL are connected to the sense amplifiers SA of the row ofsense amplifiers 12 on the right side, and they are arrangedalternately. Further, in the dummy mat 11, the bit lines /BL areconnected to the sense amplifiers SA of the row of sense amplifiers 12on the right side, and the dummy bit lines DBL are connected to a lineof a precharge potential VBLP. The arrangement of the dummy bit linesDBL corresponds to a portion where no sense amplifiers SA is arranged inthe row of sense amplifiers 12.

Further, a resistance element Rrb is connected in series between eachbit line /BL and each sense amplifier SA in the dummy mat 11. Theresistance element Rrb is formed, for example, using a diffusiveresistance, and resistance values of the bit line /BL and the resistanceelement Rrb are set to be equal to a value of a bit line resistance Rbin the normal memory mat 10.

By employing the configuration of the embodiment, the capacitance valueand the resistance value of one bit line BL can be substantially thesame as those of the other bit line /BL when the sense amplifier SA ofthe row of sense amplifiers 12 is operating. In practice, the number ofdummy cells DC arranged in the dummy mat 11 can be remarkably smallerthan the number of memory cells MC arranged in the normal memory mat 10,and thereby the area of the dummy mats 11 can be drastically reduced.For example, in the configuration of FIG. 1, N word lines WL arearranged in the normal memory mat 10 while four dummy cell control linesDCL are required in the dummy mat 11, so that a sufficient effect ofreducing the area can be obtained particularly when N is large. Further,since the structure of the dummy mats 11 is common to that of the normalmemory mats 10, there is a merit that applying a complicated processtechnique can be avoided.

Returning to FIG. 1, sub-word drivers (SWD) 13 are arranged on bothsides of each normal memory cell 10 in the Y direction. Each sub-worddriver 13 selectively connects each sub-word line (word line WL) in thenormal memory mat 10 to a common main word line (not shown) extending inthe Y direction. Switch circuits (SW) 14 are arranged on both sides ofeach row of sense amplifiers 12 in the Y direction. Each switch circuit14 selectively connects a signal transmitted via the row of senseamplifiers 12 to input/output lines.

Next, control and operation of the memory cell array in the DRAM of theembodiment will be described with reference to FIGS. 3 to 6. FIG. 3shows an example of a schematic circuit block diagram of the DRAM of theembodiment. The DRAM shown in FIG. 3 includes four banks (0 to 3) havingthe same size and function. The memory cell array shown in FIG. 1 isformed in each bank. Although the circuit block diagram of FIG. 3 issimplified, the memory cell array in each bank includes a plurality ofnormal memory mats 10 aligned in the bit line extending direction anddummy mats 11 at both ends thereof. Further, a row decoder 24 selectinga predetermined word line is provided attached to the memory cell array.

As shown in FIG. 3, there are provided a command decoder 20, an addressbuffer 21 and a mode circuit 25, which are common to the four banks. Thecommand decoder 20 generates a command signal in response to a controlsignal and a bank selection signal which are inputted from outside, andsupplies the command signal to a bank to be accessed. The address buffer21 buffers an externally inputted address, and sends the address to eachbank. The mode circuit 25 supplies a dummy cell selection signal S1 andan operation selection signal S2 to the dummy mats 11 of each bank. Themode circuit 25 may be replaced with a fuse circuit having the samefunction. In addition, operation control of the dummy mats 11 based onthe dummy cell selection signal 51 and the operation selection signal S2will be described later.

Each bank further includes a control circuit 22 and an address latch 23.The control circuit 22 controls the operation of the bank in response tothe command signal, and supplies various control signals such as starttiming signals for the word line WL and the sense amplifier SA tovarious parts in the bank. The address latch 23 supplies the addressfrom the address buffer 21 to the row decoder 24 and the memory cellarray in response to a latch signal received from the control circuit22.

FIG. 4 is a partially enlarged block diagram showing the memory cellarray and its peripheral part in an arbitrary bank for the purpose ofexplaining the control of each dummy mat 11 of FIG. 3. In FIG. 4, thenormal memory mats 10, the dummy mat 11, the rows of sense amplifiers12, the sub-word drivers 13 and the switch circuits 14 are the same asthose in the configuration of FIG. 1, so description thereof will beomitted. Meanwhile, in FIG. 4, there are provided main word drivers 30for driving the main word lines 30 and main word controllers 31 forcontrolling the operation of the main word drivers 30, which arerespectively attached to a plurality of memory mats 10 aligned in the Ydirection. Similarly, there are provided a main dummy cell control linedriver 30 a for driving the main dummy cell control lines, a main dummycell control line controller 31 a for controlling the operation of themain dummy cell control line driver 30 a, and a selector unit 32 forselecting the operation of the main dummy cell control line controller31 a, which are respectively attached to a plurality of dummy mats 11aligned in the Y direction. There are further provided a sub dummy cellcontrol line driver 13 a for selectively controlling the dummy cellcontrol lines DCL of each of dummy mats 11 having a common main dummycell control line.

As shown in FIG. 4, a mat selection signal SMAT, a word line set signalSWL and a word line reset signal RWL respectively supplied by thecontrol circuit 22 are sent to the main word controller 31 attached tothe normal memory mat 10 and are sent to the selector unit 32 attachedto the dummy mat 11. A dummy cell selection signal S1 is also suppliedfrom the mode circuit 25 to the dummy cell control line controller 31 aattached to the dummy mat 11. As shown in FIG. 2, when the four dummycell control lines DCL are provided, the dummy cell selection signal 51of 2 bits needs to be used. Meanwhile, the selector unit 32 includesselectors which receive the mat selection signal SMAT, the word line setsignal SWL and the word line reset signal RWL respectively, and eachselector is controlled in response to the operation selection signal S2supplied from the mode circuit 25 (or the fuse circuit).

In the configuration of FIG. 4, circuit configurations of the sub dummycell control line driver 13 a, the main dummy cell control line driver30 a and the main dummy cell control line controller 31 a, which areattached to the dummy mat 11, are common to those of the sub-word driver13, the main word driver 30 and the main word controller 31, which areattached to the normal memory mat 10. Thus, it is advantageous that thecontrol of the dummy mat 11 can be shared with the control of the normalmemory mat 10.

FIG. 5 is a first operation waveform diagram explaining the control ofthe dummy mat 11. The first operation waveform diagram includeswaveforms of a selected word line WL(A) of a normal memory mat 10(A)which is not adjacent to the dummy mat 11, a selected word line WL(B) ofa normal memory mat 10(B) adjacent to the dummy mat 11, four dummy cellcontrol lines DCL(0) to DCL(3) of the dummy mat 11, and one pair of bitlines BL and /BL read out to the sense amplifier SA. In addition, aninitial voltage of each dummy cell DC of the dummy mat 11 is assumed tobe set to the precharge potential VBLP in an initial state.

At a timing t0, the normal memory mat 10(A) is selected by an ACTcommand. Thereby, the selected word line WL(A) is driven, and is resetby a PRE command at a timing t1 after a predetermined period is elapsed.At this point, each of the dummy cell control lines DCL(0) to DCL(3) ismaintained at a low level. On the other hand, when the normal memory mat10(B) is selected by the ACT command at a timing t2 so that the selectedword line WL(B) is driven, two (the second predetermined number of theinvention) dummy cell control lines DCL(0) and DCL(1) are simultaneouslyactivated to a high level. Since the bit line capacitance Cb of thenormal memory mat 10 is assumed to be 50 fF and the cell capacitance Csof the dummy cell DC is assumed to be 25 fF, two dummy cells DCconnected to the bit line /BL are turned ON by two dummy cell controllines DCL(0) and DCL(1), and therefore the pair of bit lines BL and /BLinputted to the sense amplifier SA become to have the same capacitancevalue.

As shown in FIG. 5, after the timing t2, a minute potential of thememory cell MC of the normal memory mat 10 is read out to the bit lineBL, and subsequently amplified by the sense amplifier SA. At this point,the level of the bit line BL gradually increases to a voltage VARY, andthe level of the bit line /BL which forms the complementary pair withthe bit line BL gradually decreases to a voltage VSSSA. Then, when theselected word line WL is reset by the PRE command at a timing t3, thepair of bit lines BL and /BL returns to the precharge potential VBLPagain. Since the pair of bit lines BL and /BL have substantially thesame resistance value and the same capacitance value, operationwaveforms thereof symmetrically change with polarities reverse to eachother. Thereafter, the dummy cell control lines DCL(0) and DCL(1) arereset at the low level at a timing t4. In addition, a delay time betweentimings t3 and t4 is set to a time required for stabilizing the pair ofbit lines BL and /BL to the precharge potential VBLP.

Next, FIG. 6 shows a second operation waveform diagram explaining thecontrol of the dummy mat 11. The second operation waveform diagramincludes waveforms common to those of the first operation waveformdiagram of FIG. 5, however four dummy cell control lines DCL(0) toDCL(3) are controlled in a different manner. That is, the dummy cellcontrol lines DCL(0) and DCL(1) are continuously maintained at a highlevel from an initial point. Thus, two dummy cells DC connected to thebit line /BL by the dummy cell control lines DCL(0) and DCL(1) arealways ON. Therefore, since the time between timings t3 and t4 in FIG. 5is not required, high-speed operation can be correspondingly expected.The control in FIG. 6 allows the dummy cell control lines DCL to becontrolled simply. In FIG. 6, other operation waveforms are the same asthose in FIG. 5, so description thereof will be omitted.

Next, a layout of the memory cell array of the DRAM of the embodimentwill be described. FIG. 7 shows an example of a partial layout of anarea including the dummy mat 11 in the memory cell array. The layoutshown in FIG. 7 includes the area where two bit lines /BL and two dummybit lines DBL extending in the X direction intersect with four dummycell control lines DCL extending in the Y direction. The bit lines /BLand the dummy bit lines DBL are arranged in parallel with the same pitchin an upper wiring layer. A plurality of diffusion layers 40 are formedin a lower layer in FIG. 7, and each of the diffusion layers 40corresponds to two dummy cells DC. Each of the two dummy cell controllines DCL intersecting with the diffusion layers 40 functions as gateelectrodes, which partitions a central source region located between twogate electrodes and two drain regions on both sides of the sourceregions.

In each diffusion layer 40, a first contact 41 is formed on the sourceregion, and second contacts 42 are formed on the two drain regions. Thefirst contact 41 consists of a lower cell contact and an upper bit linecontact, and each of the second contacts 42 consists of a lower cellcontact and an upper capacitance contact. The source region and theupper bit line /BL or the upper dummy bit line DBL are connected via thefirst contact 41, and the drain regions and upper electrodes of thecapacitors Cs are connected via the second contact 42.

A diffusive resistance 43 functioning as the above-mentioned resistanceelement Rrb is formed at one end of each bit line /BL. Third contacts 44a and 44 b are formed on both ends of the diffusive resistance 43. Theboth ends of the diffusive resistance 43 and the upper bit line /BL areconnected via the third contacts 44 a and 44 b, and a path from the bitline /BL to the bit line /BL at the side of the sense amplifier SA isformed through the third contact 44 a, the diffusive resistance 43 andthe third contact 44 b. Thereby, the diffusive resistance 43 as theresistance element Rrb is connected in series in the bit line /BL of thedummy mat 11. In addition, the structure of the resistance element Rrbis not limited to the diffusive resistance 43 and may be formed in otherstructures.

In the embodiment, the layout of the dummy mat 11 shown in FIG. 7 can becommonly used for the layout of the normal memory mat 10. That is, inthe normal memory mat 10, the word lines WL are arranged in the samemanner as the dummy cell control lines DCL in FIG. 7, and the diffusionlayers corresponding to the memory cells MC have the same structure asthat of the diffusion layers 40 of FIG. 7. Accordingly, the dummy mats11 can be formed without a complicated manufacturing process, and it ispossible to minimize load in manufacturing process.

In the foregoing, the present invention has been specifically describedbased on the embodiment, however the present invention is not limited tothe above embodiment, and various modifications can be applied to thepresent invention without departing from the scope of the presentinvention. That is, the present invention can be applied tosemiconductor memory devices capable of achieving the same function withvarious structures.

1. A semiconductor memory device having an array structure of an openbit line structure, comprising: a plurality of normal memory mats eachincluding a plurality of memory cells, the normal memory mats aligned atleast in a bit line extending direction; two dummy mats each including aplurality of dummy cells, the dummy mats arranged in a bit lineextending direction at both ends of the plurality of normal memory mats;and a plurality of rows of sense amplifiers arranged between the normalmemory mats and between each of the normal memory mats and each of thedummy mats, wherein a first predetermined number of the dummy cells, thenumber of which is smaller than a number of the memory cells arrangedalong each bit line of the normal memory mats, are arranged along eachbit line of the dummy mats.
 2. The semiconductor memory device accordingto claim 1, wherein a resistance element is connected in series betweeneach bit line of the dummy mats and each sense amplifier of the row ofsense amplifiers adjacent to the dummy mat, and a resistance of the bitline of the dummy mats and a resistance of the resistance element aresubstantially equal to a resistance of the bit line of the normal memorymats.
 3. The semiconductor memory device according to claim 2, whereinin each of the dummy mats, the bit lines each connected to the senseamplifier via the resistance element and dummy bit lines not connectedto the sense amplifier are alternately arranged, and the firstpredetermined number of the dummy cells are arranged along each of thebit lines and each of the dummy bit lines.
 4. The semiconductor memorydevice according to claim 3, wherein a line for supplying a prechargepotential is connected to each of the dummy bit lines.
 5. Thesemiconductor memory device according to claim 1, wherein dummy cellcontrol lines of the first predetermined number each having a samestructure as a word line of the normal memory mat are arranged in thedummy mat, and switching of the dummy cells is controlled in response tolevels of the dummy cell control lines.
 6. The semiconductor memorydevice according to claim 5, wherein the dummy cell control lines of thefirst predetermined number are capable of being selectively driven, andthe bit lines of the dummy mat in a state in which a secondpredetermined number of dummy cells of the first predetermined number ofthe dummy cells are turned on have an approximately same capacitance asa bit line capacitance of each bit line of the normal memory mats. 7.The semiconductor memory device according to claim 6, wherein a modecircuit or a fuse circuit is provided for individually controlling thelevels of the first predetermined number of dummy cell control lines. 8.The semiconductor memory device according to claim 7, wherein when thenormal memory mat adjacent to the dummy mat operates, control isperformed so that each of the second predetermined number of dummy cellcontrol lines is activated at a driving timing of a selected word lineof the normal memory mat and is deactivated after a predetermined delaytime is elapsed from a reset timing of the selected word line.
 9. Thesemiconductor memory device according to claim 7, wherein when thenormal memory mat adjacent to the dummy mat operates, control isperformed so that each of the second predetermined number of dummy cellcontrol lines is always activated.
 10. The semiconductor memory deviceaccording to claim 1, wherein each of the dummy cells has the same sizeand structure as each of the memory cells.
 11. The semiconductor memorydevice according to claim 1, wherein both the dummy cells and the memorycells are commonly formed with a cell size of 6F².
 12. A semiconductordevice comprising: a plurality of sense amplifiers each including firstand second sense nodes; a plurality of first lines each connected to thefirst sense node of an associated one of the sense amplifiers; aplurality of second lines; a plurality of resistive elements eachconnected between an associated one of the second lines and the secondsense node of an associated one of the sense amplifiers; a plurality ofthird lines intersecting the first lines; a plurality of first memorycells each disposed at an associated one of intersections of the firstlines and the third lines; at least one fourth line intersecting thesecond lines; and a plurality of second memory cells each disposed at anassociated one of the second lines and the fourth line.
 13. The deviceas claimed in claim 12, wherein the at least one fourth line is smallerin number than the third lines so that the second memory cells aresmaller in number of the first memory cells.
 14. The device as claimedin claim 13, wherein the sense amplifiers are arranged in line in afirst direction and each of the first and second lines is elongated in asecond direction crossing the first direction.
 15. The device a claimedin claim 12, further comprising a plurality of fifth lines which aremixed with the second lines and supplied with a predetermined potential.16. A semiconductor device comprising: a plurality of memory arraysarranged in line in a first direction, the memory arrays therebyincluding a first end memory array, a second end memory array and atleast one intermediate memory array between the first and second endmemory arrays; and a plurality of sense amplifier sets, each of thesense amplifier sets being between associated adjacent ones of thememory arrays and including a plurality of sense amplifiers arranged inline in a second direction crossing the first direction; the at leastone intermediate memory array including: a plurality of first bit lineseach extending in the first direction and belonging to one of the senseamplifier sets, a second bit lines each extending in the first directionand belonging to a different one of the sense amplifier sets, aplurality of first word lines each extending in the second direction tocross the first and second bit lines, and a plurality of first memorycells each disposed at an associated one of crossing points of the firstword lines and the first and second bit lines; each of the first andsecond end memory arrays including: a plurality of third bit lines eachextending in the first direction and belonging to one of the senseamplifier sets, a second fourth lines each extending in the firstdirection and belonging to no one of the sense amplifier sets, aplurality of second word lines each extending in the second direction tocross the third and fourth bit lines, and a plurality of second memorycells each disposed at an associated one of crossing points of thesecond word lines and the third and fourth second bit lines, the secondmemory cells being smaller in number than the first memory cells of theat least one of the intermediate memory array.
 17. The device as claimedin claim 16, wherein each of the first and second end memory arraysfurther includes a plurality of resistive elements each connectedbetween an associated one of the third bit lines and an associated oneof the sense amplifiers of the one of the sense amplifier sets.
 18. Thedevice as claimed in claim 16, wherein one of the first word lines ofthe at least one intermediate memory array is activated with activatingat least two of the second word lines of one of the first and second endmemory arrays.
 19. The device as claimed in claim 18, wherein each ofthe first and second end memory arrays further includes a plurality ofresistive elements each connected between an associated one of the thirdbit lines and an associated one of the sense amplifiers of the one ofthe sense amplifier sets.